The present invention relates to a four-wheel driving apparatus with an automatic transmission for vehicles, and more particularly to an arrangement of a driving system for front of a vehicle and a driving system for the rear wheels of the vehicle.
This kind of driving apparatus is disclosed in Japanese patent application laid-open No. 56-43031. In the disclosed apparatus, the driving system for the front wheels is constructed as a main driving system and driving system for the rear wheels is arranged to be selectively coupled to the main driving system. A final reduction gear device for the front wheels is disposed between a torque converter and an automatic transmission device. An output shaft connected to a planetary gear device is extended forwardly and operatively connected to a pinion shaft for the final reduction gear device through a drive gear and driven gear, thereby driving the front wheels.
In order to transmit the output of the automatic transmission to the rear wheels, the pinion shaft is connected to a transfer drive shaft. The transfer drive shaft extends rearwardly passing through a space formed beneath the planetary gear device and brake and clutch devices. The rear end portion of the transfer drive shaft is connected to a rear drive shaft through transfer gears and a clutch for transmitting the output to the rear wheels.
Therefore, the pinion shaft must transmit the output to both of the front wheels and the rear wheels, which will overload the shaft on the power transmission.
In addition, since the transfer drive shaft must extend between the brake and clutch devices and an oil supply control device, the construction is complicated. Further, the oil supply control device vibrates with the rotation of the transfer drive shaft, causing the oil pressure control to malfunction.
Since the transfer drive shaft is in a lower position, the transfer gears are provided to connect the transfer drive shaft with the rear drive shaft which is in a higher position. In addition to the transfer gears, a clutch for driving the rear wheels is positioned adjacent the transfer gears. Therefore, a large space for the transfer gears and clutch must be provided on the rear side of the automatic transmission. The enlarged rear portion of the automatic transmission extends into the passenger's compartment of the vehicle thereby decreasing the capacity of the compartment.